The performance of an internal combustion engine is dependent on a number of factors including the operating cycle (e.g., two-stroke having 360 degrees of crankshaft rotation per cycle, four-stroke having 720 degrees of crankshaft rotation per cycle, or Wankel), the fuel type (e.g., gasoline or diesel) the number and design of combustion chambers, the selection and control of ignition and fuel delivery systems, and the ambient conditions in which the engine operates. Examples of design choices for a combustion chamber are believed to include choosing a compression ratio and choosing the numbers of intake and exhaust valves associated with each chamber.
With regard to fuel delivery systems, carburetors and fuel injection systems are known. Those known systems supply a quantity of fuel, (e.g., gasoline and air), in accordance with the position of the throttle as set by the operator. In the case of carburetors, fuel is often delivered by a system of orficies, known as “jets.” As examples of carburetor operation, an idle jet may supply fuel downstream of a throttle valve at engine idling speeds, and that fuel delivery may be boosted by an accelerator pump to facilitate rapid increases in engine load.
Known fuel injection systems, which can be operated electronically, spray a precisely metered amount of fuel into the intake system or directly into the combustion cylinder. The fuel quantity is typically determined by a controller based on the state of the engine and a data table known as a “map” or “look-up table.” The map typically includes a collection of possible values or “setpoints” for each of at least one independent variable (i.e., a characteristic of the state of the engine), which can be measured by a sensor connected to the controller, and a collection of corresponding control values, for a dependent variable control function, e.g., fuel quantity.
Further, engine performance is substantially dependent on how combustion is accomplished in the ambient conditions. The stoichiometric mass fraction ratio of air to gasoline is approximately 14.7:1. However, it is believed that ratios from about 10:1 to about 20:1 will combust, and that it is often desirable to adjust the air-fuel ratio (“AFR”) to achieve specific engine performance (e.g., a certain level of power output, better fuel economy, or reduced emissions). Properly calibrating the fuel delivery system of the engine to deliver the optimum AFR under all operating conditions is important to optimum engine operation.
Vehicles are commonly manufactured having carburetors. Often, those carburetors provide high quality air flow control through, for example, a butterfly or gate type air valve. Those carburetors, however, may not provide high quality fuel delivery through a float bowl and jets. For example, an amount of fuel supplied through a fuel injector may change more rapidly in response to throttle position than the amount of fuel supplied through a float bowl and jets.
Because the quality of fuel delivery provided by a carburetor is often not as great as fuel injectors, vehicle owners desiring high quality fuel delivery often replace vehicle carburetors with throttle body fuel injectors that deliver both fuel and air to the vehicle engine. Such replacement is, however, typically expensive both in the cost of replacement parts and labor to perform the replacement. The air delivery component of the throttle body fuel injector may, furthermore, constitute a large part of the cost of replacement parts. Thus, there is a need for an apparatus and method that provides fuel injection in a carbureted engine system.